[Carl n Susan]

The "No Fuss" or "tank flush" system is for the black tank. It is a separate hose bib connection in the convenience center which sends water through a sprayer into the black tank. This helps to wash out "stuff" remaining after it has been dumped. The warning sticker wants you to be sure the dump valve for the black tank is OPEN when you run the tank flush. Failure to open the valve results in filling the tank and either it bursts ($$$$$) or there is an eruption of sewer content through the roof vent (hilarious for the neighbors). Experienced users do run the flush with the valve closed for a short time but it isn't without risk.

The "normal fill" or "tank fill" switch is associated with the shore water input system (not a flush system). This is how you get water into the coach. Normally you hook the water hose from the park supply to this hose bib and this provides water to the coach faucets/outlets when in the "normal fill" position. The "tank fill" position sends the input water to the fresh water holding tank. This is for when you want to use the onboard water pump to supply water to the coach.

Doing a Search on any of these terms here will provide you with hours of entertainment and education of what to do and what not to do.